\begin{tabular}{cccc}
	                          A &   B &                           C &    D \\
	                        AAA & BBB &                         CCC &  DDD \\
	\multicolumn{2}{c}{first heading} & \multicolumn{2}{c}{second heading} \\
	                        one & two &                       three & four \\
	                       five &     &                         six &      \\
	                      seven &                                          \\
\end{tabular}
